Method and device for determining the purity and/or pressure of gases for electric lamps

ABSTRACT

According to the method the intensity of at least one pressure-independent (impurity detection) or pressure-dependent (gas pressure determination) spectral line is measured selectively. Indirect detection utilizes the intensity of spectral lines whose wavelengths correspond to higher levels of excitation energy than those of the impurities. The intensity of these spectral lines is a measure of the impurities. Alternatively, the intensity of at least one spectral line of the respective impurity is measured directly. In order to eliminate co-phasal interference, two spectral lines are measured and the ratio is formed therefrom. The intensity ratio of argon lines of wavelengths λ 1  =772.4 nm and λ 2  =738.4 nm has in particular proved acceptable for the indirect detection of impurities in argon and the intensity ratio V of the argon lines of wavelengths λ 1  =763.5 nm and λ 2  =738.4 nm has proved acceptable for determining the argon pressure. The measuring process is in particular suitable for integration in high-speed production lines for discharge lamps.

FIELD OF THE INVENTION

The invention relates to a method for detecting impurities in gases,especially noble gases, or gas mixtures for electric lamps or radiatorsand to a method for measuring the pressure of gases, especially noblegases, or the gas components of gas mixtures for electric lamps orradiators. The invention also relates to an apparatus for performingthese methods.

The term "electric lamps" includes both incandescent and dischargelamps. The term "electric radiators" is understood to mean gasdischarges that emit primarily electromagnetic radiation outside thevisible range, especially in the UV or IR range.

The methods utilize the influence of the gas pressure or of impuritieson the fluorescence spectrum of a gas discharge, especially a glowdischarge.

BACKGROUND

Gaseous or vapor-form as well as solid substances whose presence ingases or gas mixtures for electric lamps or radiators--hereinaftercalled gas system for brevity--is undesired and are designated asimpurities. As a rule, these impurities enter the gas system in anuncontrolled way, for instance even during lamp production by means ofcontaminated rinsing gases or fill gases or through leaky pumping andfilling systems. Even in the finished lamp, however, impurities canenter the gas system of the lamp, for instance through leaks of the lampbulb itself or even during lamp operation, for instance throughcontaminated electrodes or increased electrode burnoff from inadequatefill pressure. The consequence of impurities--of whatever source--is inthe final analysis nonfunctional lamps, or lamps of limited service lifeor maintenance.

The goal of all these efforts is therefore to assure the least possiblecontamination of the gas system even during lamp production. Moreover,for the sake of seamless quality control it is desirable that finishedlamps with unacceptably high contamination or excessive deviations fromthe desired fill pressure be detected and rejected. With thisbackground, rapid, reliable detection of corresponding impurities andmonitoring of the fill pressure become quite important.

One method for determining the gas purity is known from the contributionby M. Gaugel entitled "Gasreinheitstest bei Halogen-Gluhlampen mit Hilfeeines Spektrallinienvergleichs" Gas Purity Test in Halogen IncandescentLamps using Spectral Line Comparison! to the book series entitled"Technisch-Wissenschaftliche Abhandlungen der OSRAM-Gesellschaft"Technical-Scientific Treatises at OSRAM!, Vol. 12, pp. 546-549,Springer-Verlag, Berlin 1986. There, the light of halogen incandescentlamps is split by two beam splitters into three beams of light anddelivered to three spectrally differently sensitive photomultipliers.The maximum spectral sensitivity of the individual photomultipliers islocated at the wavelength of about 410 nm, 523 nm and 616 nmrespectively, that is, in the blue, green and red range of theelectromagnetic spectrum. By means of two analog dividers, the ratios ofthe "red/blue" and "red/green" photomultiplier signals are formed andcompared by two comparators to find whether the corresponding values arewithin preadjustable tolerance range. If not, the halogen incandescentlamp is found to be defective; that is, either a fill error and/orexcessive gas contamination has occurred.

A disadvantage of this embodiment is that the halogen incandescent lampto be tested must, including its optical setup and photomultipliers, belocated inside an opaque housing during the measurement. Otherwise,in-phase interference signals, such as ambient light, cause incorrectmeasurements, since these interference signals are weighted spectrallycompletely differently by the three photomultipliers and are thereforenot eliminated in the quotient formation.

U.S. Pat. 4,759,630 Vuasa et al., discloses an arrangement fordetermining the quality of incandescent lamps. It includes a device forgenerating a discharge between the incandescent coil and an electrodemounted on the outer wall of the lamp bulb, and an apparatus foranalyzing the radiation emitted by the discharge in the wavelength rangebetween 550 nm and 570 nm. The lamp quality is judged from the behaviorover time of this radiation, which is optionally compared with theradiation in the wavelength range between 660 nm and 680 nm.

In U.S. Pat. 3,292,988, the intensity of spectral lines of the fill gascomponent argon that have wavelengths greater than 650 nm is used tomonitor the mercury vapor pressure in fluorescent lamps during lampoperation.

U.S. Pat. 5,168,323 proposes an apparatus and a method for determiningimpurities in a gas. The apparatus includes two opposed electrodes,between which the gas flows; a low-frequency alternating voltage sourceconnected to the electrodes; and an optimal measuring instrument. Withthe aid of the alternating voltage source, an arc discharge is generatedwhose emission lines are detected by means of the measuring instrument.From the intensities of characteristic spectral lines of the variousimpurities, their concentration is determined with the aid of a linearequation system.

THE INVENTION

A first object of the invention is to overcome the disadvantagesdiscussed and to disclose a relatively simply attainable method, whichin particular can be integrated into lamp production, for detectingimpurities in gases or gas mixtures for electric lamps or radiators. Themethod should moreover be suitable in particular for monitoring thefunction and/or quality of electric lamps.

A further object of the invention is the determination of the pressureof gases, especially noble gases, or the gas components of gas mixturesfor electric lamps or radiators. Moreover, the method should be suitablein particular also for monitoring the function and/or quality ofelectric lamps or radiators.

Still another object of the invention is provide an apparatus with whichthe proposed methods can be performed.

Briefly, by means of a gas discharge, the gas or gas components of themixture and the impurities possibly contained therein are excited toemit electromagnetic radiation. Detecting possibly admixed gaseousand/or vapor-form impurities or detecting the pressure of the gas or gascomponent is effected by means of the measured intensity of one or moresuitable spectral lines of this radiation.

In accordance with a feature of the invention, impurities are detectedby purposefully using one or more spectral lines whose intensities inthe relative pressure range, that is, fill pressures in electric lamps,are largely pressure-independent. In this way, incorrect measurementsfrom pressure fluctuations of the gas are averted. For the practicalacceptability of the method this is of major significance, especiallyfor detecting impurities in the lamp vessels of electric lamps, sincethe fill pressures of the lamps vary as a function of productionvariations. Spectral lines whose intensities are pressure-dependent cantherefore produce false results. If unlike the invention the intensityof the radiation is integrated over a relatively broad wavelength range,then in unfavorable cases pressure-dependent spectral lines can bedetected as well. The consequence is incorrect measurements, if the fillpressure fluctuates.

The concrete selection of suitable spectral lines takes into accountpossibly present gas components, such as the fill components of metalhalide high-pressure discharge lamps. Only individual spectral linesthat do not overlap or coincide with other lines of the fluorescencespectrum are selected. The permissible spacing of the selected linesfrom neighboring lines should advantageously be greater than thespectral resolution of the measurement. This prevents the intensity ofundesired lines from being measured as well and the attendantadulteration of the result.

In accordance with another feature of the invention for determining thepressure of gases, in particular noble gases, or the gas components ofgas mixtures, one or more spectral lines of the gas or applicable gascomponent is purposefully used; the intensity of at least one so usedspectral line is pressure-dependent. In a pressure range dependent onthe excitation conditions, typically from the prevacuum range toatmospheric pressure, and in particular in the range betweenapproximately 0.1 kPa and approximately 40 kPa, the intensity ofsuitable spectral lines increases with the pressure. With the aid of themeasured pressure-dependent intensity and a calibration measurementvalue, the absolute pressure of the gas or the partial pressure of thecorresponding gas component is then ascertained.

A very essential aspect of the methods in accordance with the inventionis the selective measurement of the spectral lines. It has in fact beenfound in preliminary experiments that reliable results under productiontechnology conditions can be attained only if the measurement conditionsexplained hereinafter are adhered to.

In improved variants of both methods, a quotient of the intensities oftwo spectral lines is formed, with the intensity of at least one linebeing pressure-independent. Preferably the two spectral lines are soclose together that noise signals and in-phase interference signals,especially ambient or scattered light, are assessed spectrally virtuallyidentically. The spacing of the two spectral lines is typically lessthan about 100 nm and preferably less than about 50 nm. Since theaforementioned interference signals within this spacing have a virtuallyconstant spectral intensity distribution, or in other words are presentin relatively broad bands in comparison to the selected spectral lines,they are largely eliminated in the quotient formation. In-phase signalattenuations, for instance caused in electric lamps by bulb blackening,are likewise eliminated. For these reasons, the ratio measurementdescribed (ratiometric measuring method) is to be preferred over afundamentally possible absolute measurement of the intensity of a singlespectral line, in which interference effects greatly adulterate theoutcome of measurement, which as a rule cannot be correctedretroactively.

The selection of suitable special lines for the ratio measurementdepends on the specific gas or gas components. In the case where argonis present, suitable spectral lines are in the wavelength range between650 nm and 800 nm, or between 800 nm and 1000 nm.

In a concrete embodiment of the method for detecting impurities, atleast one spectral line of the gas or of a gas component whose intensityis independent of fill pressure; is purposefully selected, and whosewavelength or wavelengths correspond to a higher excitation energy thanthat of the spectral lines of the expected impurities to be determined.Impurities that may possibly be present are consequently excitedpreferentially. In simplified terms, some of the electric power of thegas discharge enters increasingly into these "loss channels", instead ofinto the occupation of the excited states, corresponding to the selectedspectral lines, of the gas or gas components. As a result, theintensities of the selected spectral lines decrease (the correspondingoptical transitions are increasingly "quenched" by the impurities; thatis, the density of occupation of the associated excited statesdecreases), and in fact all the more so, the higher the concentration ofthe impurities ("quench partners"). For this reason, the attenuation ofthe intensities of the selected spectral lines is indirect evidence ofimpurities located inside the lamp vessel.

The advantage of this indirect method is that impurities are detectednonspecifically, or in other words in their totality. As a result, it ispossible in a simple way with only a single measurement--or two in thecase of the ratiometric variant--to detect impurities. This method istherefore particularly suitable for control and monitoring purposes, inorder to trigger suitable procedures in the event of the appearance ofimpurities. One example of this is quality control in the production ofelectric lamps, where lamp bulbs with impurities are detected andrejected. By the rapid, simple detection of impurities by measurementtechniques, this method can readily be integrated into automated,high-speed production processes.

Virtually all undesired solid impurities--such as residues from theglass forming process--and/or liquid and/or gaseous or vapor-formimpurities that can get into the lamp vessel, for instance in thepumping-out or filling process, are detected. In particular, thedetectable impurities include the elements of oxygen (O), hydrogen (H),nitrogen (N), carbon (C), silicon (Si), or compounds of these elements,such as water (H₂ O) or hydrocarbons (CH), and others. The source ofthese impurities may be leaks or defects in the pumping system (examplesbeing O, H₂ O, oil vapors) or individual contaminated components (forinstance, O from oxidized electrode surfaces, H₂ O incorporated intoelectrode surfaces or hygroscopic metal halides). Silicon can occur as afilm on the electrodes, for instance caused by defective pinches of thelamp bulb.

In lamp technology, noble gases are used, such as argon (Ar), krypton(Kr), xenon (Xe) or helium (He). These gases have spectral lines whoseexcitation energies are correspondingly high (typically greater than 10eV) and are thus suitable for the method. One further criterion for thesuitability of spectral lines is an intensity that is adequately farabove the noise. These demands are ideally met by the spectral lines ofargon, with the wavelengths γ₁ =738.4 nm, γ₂ =772.4 nm, and γ₃ =811.5nm. If the gas to be investigated comprises argon or the gas mixturecontains argon, then preferably one or more of these spectral lines areused for the method. In an individual case, optionally those spectrallines which are not covered by the lines of other fill components andtheir compounds are selected. In an especially preferred variant, thedetection is performed with the aid of the quotient of the intensitiesof the argon spectral lines having the wavelengths γ₁ =772.4 nm and γ₂=738.4 nm.

For the sake of illustrating the relationships, the following table 1shows some relevant excitation energies for argon and for the impuritiesof hydrogen (H), nitrogen (N), oxygen (O), carbon (C) and silicon (Si),along with the wavelengths of the associated spectral lines. It can beseen from this that the excitation energies of the impurities are someof them located considerably below those for argon.

                  TABLE 1    ______________________________________    Excitation energies and corresponding wavelengths of    the corresponding optical transitions for argon and some possible    impurities (quench partners).                 Excitation energy                             Wavelength    Component    in eV       in nm    ______________________________________    Ar           13.07       811.5                 13.30       738.4    H            12.09       656.3    N            11.76       868.3                 11.75       870.3    O            10.74       777.2    C            9.17        833.5                 8.85        909.4                 8.77        965.8    Si           7.60        623.7                 7.32        725.1    ______________________________________

In the case of molecular impurities, such as water (H₂ O), OH radicals,hydrocarbons, along with the electronic excitations the loss channels ofthe rotational and vibrational excitation also occur. The energiesrequired for this are in the meV range or amount to a few eV (less thanabout 3 eV) and are thus markedly less in each case than the requisiteexcitation energies for argon.

In a further concrete embodiment of the method, the intensity of one ormore spectral lines of the applicable impurity is measured purposefully.The advantage is that with the aid of this direct method the applicableimpurity can be detected specifically or in other words identified, andits concentration can be determined by means of a calibrationmeasurement. This makes it easier to find the source of the possibleimpurity, such as a defective pumping system if hydrocarbon compounds(oil vapors) appear. The disadvantage is that this direct method isrelatively complicated and expensive, since the intensity of at leastone line (or band) must be measured and evaluated for each possibleimpurity.

For determining the concentration of the molecules N₂, CN, CH or C₂, theintensities of the associated molecular bands at the wavelengths of357.7 nm, 388.34 nm, 388.9 nm and 468.48 nm or 516.5 nm, respectively,are suitable. To eliminate in-phase interference, these measurementvalues are referred to the intensity of a suitable pressure-independentspectral line. In the presence of argon, for instance, the spectral linehaving the wavelength 738.4 nm is suitable. Table 2 shows a listing ofsome typical impurities for discharge lamps. Also listed are thewavelengths suitable for detecting them directly.

                  TABLE 2    ______________________________________    Typical impurities for discharge lamps and wavelengths    suitable for their direct detection.    Impurity          Wavelength in nm    ______________________________________    H                 656.3    HgH               421.9    O                 777.2    N.sub.2           380.5; 357.7; 337.1    CN                388.4; 419.2    CH                388.9; 432.4; 431.4    C.sub.2           516.5; 473.7; 468.48    Si                302.0; 300.7    Re                346.0    W                 400.9    ______________________________________

An expanded two-stage method combines the direct and indirect measuringmethods. In the first method stage, it is first ascertained by theindirect measuring method whether any impurity is present at all. Onlyif that is the case is a qualitative and/or quantitative determinationof the individual components of the impurity performed in the secondmethod stage, by means of the direct measuring method.

A further variant of the method is used to assess the quality ofdischarge lamps, in particular metal halide high-pressure dischargelamps. In this variant, the time-dependent change in intensity of thespectral lines during the startup phase of the lamps is optionallyutilized in addition for assessing the electrode quality. To that end,by means of the lamp electrodes, a glow discharge is generated insidethe discharge vessel of the lamp. Depending on the properties andcondition of the electrode--for instance, surface, geometry,material--this glow discharge first burns at the electrode shaft, forinstance, and then migrates toward the electrode tip. The length of timerequired for it to do so depends on the quality of the electrode andtypically fluctuates between a few tenths of a second and a few seconds.It is longer in an oxidized electrode and/or an electrode contaminatedby quartz or other deposits, and in the event of an unsuitable electrodegeometry. The startup performance is also affected by impuritiespossibly located in the discharge vessel and an excessively low fillpressure of the ignition gas, such as argon. If the duration of thestartup phase and the course of intensity of the spectral lines duringthe startup phase are within predeterminable tolerance ranges, then thelamp meets the quality requirements. If not, it can be rejected asdefective or unacceptable.

In discharge lamps with solid or liquid fill components, the glowdischarge is advantageously operated only at low power and/or onlybriefly, for instance intermittently. This prevents a significantproportion of these fill components from changing to the vapor phase. Ifthey did so, spectral lines of the vapor could in fact be excited thatwould cover the spectral lines of possibly present impurities and wouldthus cause incorrect measurements.

In a concrete embodiment of the method for determining the pressure ofargon, the intensity of the spectral line having the wavelength γ=763.5nm is determined. Over a wide pressure range, in particular in the rangebetween about 0.1 kPa and about 40 kPa, the intensity of this spectralline increases with the pressure. By means of calibration measurements,the pressure is ascertained directly from the intensity. In aratiometric variant of the method, this intensity is related to themeasured pressure-independent intensity of a second spectral line. Thespectral line of argon having a wavelength of 738.4 nm is suitable forthis purpose, for instance.

A suitable apparatus for performing the method according to theinvention comprises a vessel, in which the gas or gas mixture and theimpurities possibly contained therein are located; an energy supplyunit, which is connected to the vessel via a coupling device andgenerates the gas discharge, in particular a glow discharge; aspectroscopic measurement device, which measures the intensity orintensities of the spectral line or lines; and an evaluation device,which from the measured values detects a possible impurity or identifiesspecific impurities and indicates their concentrations and/or ascertainsthe (partial) pressure of the gas or of the gas components of the gasmixture.

The vessel may for instance be a lamp bulb or a specimen vesselconnected to the pumping or gas mixing system of a lamp production line.

A high-frequency generator, for instance, is suitable as the energysupply unit. In that case, the coupling device can comprise eitherelectrodes located inside the discharge vessel, such as the lampelectrodes of a discharge lamp, or external electrodes. In the lattercase, electrodes connected to the high-frequency generator are mountedon the outer wall of the vessel. This variant is also known ascapacitive high-frequency discharge with dielectric electrodes. It issuitable also in particular for use in electric incandescent lamps, inwhich alternatively the incandescent coil itself can act as an internalelectrode. In that case, all that is additionally needed is one external(dielectric) electrode. The vessel may also be located in the interiorof a coil supplied by the high-frequency generator, so that an inductivehigh-frequency discharge takes place.

The spectral separating device in the simplest case comprises anarrow-band optical (interference) filter--typical resolutions arebetween about 5 nm and 10 nm--per spectral line to be measured.Alternatively, a spectrometer is suitable that breaks the radiation downinto its spectral components by means of dispersive elements--such asprisms or gratings--or in other words generates an optical spectrum. Afurther advantage is the higher resolution of a spectrometer--typically1 nm and below. To increase the detection limit, it may be advantageousto mount additional optical elements, such as lenses or mirrors, betweenthe vessel and the spectral separator, which serve to guide and focusthe fluorescent radiation toward the spectral separator.

The evaluation device in the simplest case has one or more detectorelements, such as photodiodes or a diode line or diode array. Thedetector elements convert the spectral components of the radiation intovoltage signals--corresponding to respective intensity. An indicatorunit renders the voltage signals visible in an analog or digitaldisplay. Moreover, the voltage signals may also be delivered to anelectronic computer, which for instance performs the quotient formationof the ratiometric variant. As a result and using the calibrationvalues, both the concentration of individual impurities and the gaspressure can then be calculated and output. To improve thesignal-to-noise ratio and/or reduce the effects of stochastic intensityfluctuations on the outcomes of measurement, it is advantageous toperform a cumulative averaging over a plurality of identical kinds ofmeasurements with the aid of a computer.

To ascertain the calibration values for the spectroscopic qualitycontrol in the production of discharge lamps, the following method hasproven itself.

In a first step, limit values for parameters are ascertained that act asa measure of the operability and performance of one lamp type, such asmetal halide high-pressure discharge lamps. Suitable lamp parameters arefor instance the ignition voltage, that is, the voltage required toignite the discharge; the startup peak voltage, that is, the value ofthe maximum that the voltage passes through after the lamp is turned onwhile a stable arc discharge is building up; the reignition peakvoltage, that is, the peak value of the alternating voltage applied tothe lamp electrodes; and the arc takeover time, that is, the length oftime between when the lamp is turned on and when the arc forms. Thevalues of these electric lamp parameters increase with increasingcontamination inside the lamp.

In the second step, in corresponding comparison measurements, the valuesof the electric lamp parameters are correlated with the spectroscopicmeasurement values. For example, lamps with defined impurities areproduced, measured spectroscopically, and associated with theascertained corresponding lamp parameters. In this way, a set of rangesof values for the spectral intensities or intensity ratios can beproduced for every lamp type and for various degrees of contamination.This set is then used as a reference in an actual determination of thecontamination of a lamp or a lamp fill. If the actual measuredvalues--or the ratios calculated from them are within the respectivetolerance range, the contamination is slight; if not, it isunacceptable, and the applicable lamp is rejected, or production isdiscontinued in order to correct the source of the contamination.

A major advantage of spectroscopic quality control is the rapidity ofthe measurements on which it is based. The result is typically availablewithin only a few seconds. In contrast to this, ascertaining theelectric lamp parameters in the context of calibration in thespectroscopic method takes up to several minutes (for example, up to sixminutes is tolerated as a limit value for the arc takeover time; thatis, one might have to wait that long before the applicable lamp isrejected).

The rapidity predestines the method of the invention for use inhigh-speed lamp production lines. One variant contemplates theintegration of the spectroscopic measurement method into the lampproduction process as follows. The fundamental concept here is tointroduce rapid spectroscopic online controls into the essentialproduction steps. As a result, impurities are possibly already detectedin an early phase of the course of production, rather than only in thefinished product as has been typical until now. Consequently--especiallyin high-speed production lines--the rejection rate can be reducedmarkedly.

Preferably, spectroscopic measurements are performed in the followingthree production stages:

1. before filling of the discharge vessel of the lamp and beforeelectrode installation, by means of discharge in a specimen vesselconnected to the vacuum ring line, in order to monitor the gas system ofthe production line for impurities;

2. after the insertion of the electrodes into the discharge vessel, bymeans of specimen discharge inside the discharge vessel, in particularby means of specimen discharge between the lamp electrodes, for checkingthe electrode system and the inner wall of the discharge vessel forimpurities; and

3. after the filling and closure of the discharge vessel, by means ofspecimen discharge inside the discharge vessel, in particular by meansof specimen discharge between the lamp electrodes, to check whether theimpurities inside the finished lamp are within a predeterminabletolerance range. If the measured values are within the tolerance range,the applicable discharge vessel or the corresponding complete lamp isreleased for its intended use; if not, it is rejected.

DRAWINGS

The invention will be described in further detail below in terms ofseveral exemplary embodiments. Shown are:

FIG. 1, a schematic illustration of an apparatus for the spectroscopicdetection of impurities and for determining the gas pressure in aspecimen vessel;

FIG. 1A is a fragmentary schematic illustration of an alternativeapparatus for use with an incandescent lamp;

FIG. 2, the ratio, ascertained with the apparatus of FIG. 1, between theintensities of two spectral lines of argon having the wavelengths 763.5nm and 738.4 nm as a function of the argon fill pressure in the specimenvessel 1;

FIG. 3, a schematic illustration of an apparatus of the spectroscopicdetection of impurities inside the discharge vessel of a lamp.

DETAILED DESCRIPTION

FIG. 1 shows a schematic illustration of an apparatus for performing themethod for detecting and determining the concentration of impurities andfor determining the gas pressure in a specimen vessel. The apparatuscomprises a tubular specimen vessel 1 (shown schematically in crosssection) of glass; a solid rectangular block 2 of Teflon® that partlysurrounds the specimen vessel 1; two metal pinlike electrodes 3, 4 thatprotrude partway into the block 2, where they are located diametricallyopposite one another on the outer wall of the specimen vessel 1; ahigh-voltage transformer 5, whose primary winding 6 is connected to ahigh-frequency generator 7 and whose secondary side 8 is connected tothe electrodes 3, 4; a trigger pulse generator 9, which is connected tothe high-frequency transmitter 7; an optical waveguide 10, whose firstend protrudes into part of the block 2 and is located in the vicinity ofthe outer wall of the specimen vessel 1; an ordering filter 11 locatedimmediately before the face end of the first end of the opticalwaveguide 10; an optical spectrometer 12, whose input is connected tothe second end of the optical waveguide 10 and whose output is connectedto a computer 13; and a metallic shielding housing 14, which surroundsthe block 2 with the specimen vessel 1, the electrodes 3, 4, theordering filter 11 and the high-voltage transformer 5, the opticalwaveguide 10 and the connecting cable between high-voltage transformer 5and the high-frequency transmitter 7 being extended throughcorresponding openings in the shielding housing 14 into its interior.

The diameter of the tubular specimen vessel 1 is approximately 20 mm. Ithas one metal flange on each of its two face ends (the flange is notshown in the schematic cross-sectional view of the specimen vessel 1).By means of the metal flanges, the previously evacuated specimen vessel1 is connected during lamp production, typically to a gas filling andpumping system 30 or a gas-filled production cell--also called a"glovebox"--and filled with the working or filling gas or gas mixture.The double arrows at the connecting line 31 indicate that vacuum can beapplied, gas introduced, and that the pressure conditions and fillpressures are measured. The gas or gas mixture in the interior of thespecimen vessel 1 is ionized with the aid of the electrodes 3, 4, thehigh-voltage transformer 5 and the high-frequency transmitter 7. To thatend, the high-frequency transmitter 7 furnishes an alternating voltageat a frequency of approximately 120 kHz, which by means of thehigh-voltage transformer 5 attains a peak-to-peak value of up to 49 kVbetween the electrodes 3, 4. The maximum power coupling into the gasdischarge is approximately 200 W. The high-frequency transmitter 7 istriggered by the trigger pulse generator 9. Some of the fluorescentradiation of the gas discharge is fed into the optical waveguide 10 viathe ordering filter 11, which transmits only radiation above about 300nm. This radiation is delivered to the spectrometer 12, which has afocal length of 0.5 m and a grating (not shown) with 100 lines permillimeter. The spectrum generated by the grating is projected onto adiode array (not shown). The individual diodes of the array convert theradiation intensities of narrow wavelength ranges of 0.5 nm incorresponding voltage signals. The voltage signals are carried to thecomputer 13 for further processing in accordance with the methods of theinvention.

FIG. 1A shows, schematically, an incandescent lamp 1a with anincandescent coil 25 therein, connected by a lamp lead 26 to electrode4a, corresponding to electrode 4 (FIG. 1), but which need not contactthe lamp at the outside as does electrode 4 in FIG. 1. Only one externaldielectric electrode 3 is needed.

FIG. 2 shows as an example the measurement outcomes, attained with theapparatus of FIG. 1, for various argon fill pressures. It shows theratio V of the intensities of two spectral lines of argon, having thewavelengths 763.5 nm and 738.4 nm, in arbitrary units as a function ofthe argon fill pressure p in kPa in the specimen vessel 1 of FIG. 1. Ascan be seen from FIG. 2, the ratio increases initially steadily with thepressure. Beyond a pressure of approximately 20 kPa, the ratio remainssubstantially constant over a wide pressure range. The reason for thisis the electrode voltage limited to 49 kV. As comparison measurementswith a piezoresistive manometer show, the pressure can be determinedwith the apparatus of FIG. 1 and the method described with an accuracyof 5% up to an argon fill pressure of approximately 20 kPa.

FIG. 3 schematically shows an apparatus for performing the method fordetecting impurities inside the discharge vessel of a lamp. Theapparatus comprises a metal halide high-pressure discharge lamp 15; ahigh-frequency generator 16 that is connected to the electrodes of thelamp 15 and triggered by a trigger pulse generator 17; a semitransparentmirror 18; two interference filters 19, 20, each with a photodiode 21,22 following it--the first interference filter 19 including theassociated photodiode 21 facing the transmitting side of the mirror 18and the second interference filter 20 including the associatedphotodiode 22 facing the reflective side; a two-channel volt meter 23connected to the photodiodes 21, 22; and a computer 24, which isconnected to the two channels of the volt meter 23.

With the aid of the high-frequency transmitter 16, a low-power glowdischarge, typically from a few tenths of a watt to several watts, isignited for a brief period of time, typically a few tenths of a secondto several seconds. As a result, on the one hand the ignition gas,argon, and the possibly present impurities inside the lamp 15 areexcited to fluorescence; on the other, however, a significant excitationof the remaining fill components of the lamp is prevented. Theinterference filters 19 and 20 are transparent only for radiation in arange of ±2 nm around the wavelength of about 738.5 nm or 772.4 nm. Thephotodiodes 21, 22 generate voltage signals, each corresponding to theintensity of the spectral radiation components, and these signals aremeasured by the two channels of the volt meter 23. The computer 24 readsoff the two channels, calculates the ratio of the corresponding voltagevalues, and from that and by means of a calibration value ascertains afigure of merit. If the figure of merit is within a tolerance range, thelamp 15 meets the quality requirements. If not, it is rejected asdefective on the basis of unacceptable impurities.

The invention is not limited to the exemplary embodiments described. Inparticular, individual characteristics of various exemplary embodimentsmay also be combined with one another.

We claim:
 1. A method for detecting impurities in gases, especiallynoble gases, or gas mixtures for at least one electric lamp or lamps orradiators,comprising the steps of exciting, by means of a gas discharge,the gas or gas components of the gas mixture and the impurities possiblycontained in the lamps, or said gas or gas mixture to emitelectromagnetic radiation extending over a radiation spectrum; andcomprising, in accordance with the invention, the steps of determiningany possibly present impurities in said gases or gas mixtures byselecting, within a spectral portion of said radiation spectrum, atleast one spectral line having an intensity which is largely independentof pressure in the relevant region of pressures of gases or gasmixtures, for said electric lamp or lamps or radiators, and measuringthe intensity of the so selected spectral line or lines and therebydetermining any possibly present impurities.
 2. The method of claim 1,wherein said selection step comprises selecting the spectral line orlines of the gas or gas components whose wavelength or wavelengthscorrespond to a higher excitation energy than that of the impuritiesexpected to be detected.
 3. The method of claim 2, wherein the gas orgas mixture comprises argon, and said selecting step comprises selectingone or more of the spectral lines of argon having the wavelengths of738.4 nm, 772.4 nm, 811.5 nm.
 4. The method of claim 1, wherein saidselection step comprises selecting a spectral line of an expectedimpurity; andwherein said measuring step comprises measuring theintensity of said spectral line as a measure for the concentration ofthe impurity.
 5. The method of claim 1, wherein said possible impuritiescomprise at least one of the molecules N₂, CN, CH or C₂, or acombination of said molecules.
 6. The method of claim 4, wherein thewavelengths of said expected impurities are 357.7 nm, 388.34 nm, 388.9nm and 468.48 nm or 516.5 nm, andwherein each of said wavelengths is aspectral fragment of a molecular band of the molecules of at least oneof said impurities.
 7. The method of claim 4, wherein said gas or gasmixture comprises or contains argon; andthe spectral intensity of theexpected impurity is standardized to the intensity of argon in apressure region in which the spectral intensity of argon is largelyindependent of pressure.
 8. The method of claim 7, wherein thewavelength of the argon spectral line is 738.4 nm.
 9. The method ofclaim 1, wherein said selection step comprises selecting two spectrallines which are close together, and said measuring step comprisesforminga quotient of the intensity of said two closely adjacent spectral lines,so that noise signals and in-phase interference signals are largelyeliminated by the adjacent position of said spectral lines in the courseof the formation of the quotient.
 10. The method of claim 9, whereinsaid two spectral lines are so spaced that the difference in wavelengthis less than about 100 nm.
 11. The method of claim 10, wherein thedifference in wavelengths of the two spectral lines is less than about50 nm.
 12. The method of claim 9, wherein said selection step comprisesselecting spectral lines with wavelengths in the range of between 650 nmand 1000 nm to form said quotient.
 13. The method of claim 11, whereinsaid gas or gas mixture comprises or contains argon, andwherein saidselection step comprises selecting the spectral lines of the argonhaving the wavelengths of λ₁ =772.4 nm and λ₂ =738.4 nm, from whichspectral lines the quotient of the intensities is formed.
 14. The methodof claim 1, wherein said step of exciting the gas mixture comprisesexciting the gas mixture to generate to the extent of generating a glowdischarge within the respective electric lamp or radiator.
 15. Themethod of claim 1, wherein said step of exciting the gas or gascomponents by means of a gas discharge comprises generatingelectromagnetic energy of high frequency and applying said so generatedhigh-frequency energy to said gas or gas components.
 16. The method ofclaim 1, wherein said step of exciting the gas or components by means ofa gas discharge comprises generating a gas discharge within the interiorof a high-pressure discharge lamp;measuring the duration until said atleast one spectral line has reached a quasi-steady state value after astart-up phase of the lamp; and ascertaining at least one impurity ofthe gas or gas mixture within the lamp and forming the lamp fill, andelectrode quality as a function of the magnitude of the intensity ofsaid at least one spectral line, and, optionally, further the durationuntil the intensity of said at least one spectral line has reached aquasi-steady state value after the start-up phase of the lamp.
 17. Themethod of claim 1, wherein said gas or gas mixture and forming a lampfill are retained within the interior of a discharge lamp, and said gasor gas mixture is excited to form a gas discharge therein; andfurtherincluding the following steps:a) ascertaining electrical parameters ofthe lamp that are characteristic for the operability and performance ofsaid lamp; b) then carrying out said selecting and measuring steps bymeasuring said intensity of said at least one spectral line andascertaining electrical parameters of the lamp by repeating saidascertaining steps and spectral line measuring steps for variouslyimpurity contaminated lamps, optionally including lamps that, due toimpurities, have poor ignition or are incapable of igniting or forming astable arc discharge or, if so, only with out-of-design parameter delay;and c) associating the electrical values to corresponding spectroscopicvalues, to obtain a set of calibrated reference values of spectralintensities, or intensity ratios, to permit spectroscopic assessment ofthe quality of lamps having said ascertained electrical parameters. 18.A method for determining the pressure of gases, especially noble gases,and forming a fill for electric lamps or radiators, or of gas componentsor gas mixtures for said fill,comprising the steps of exciting, by meansof a gas discharge, the gas or gas components of the gas mixtures, andof impurities possibly contained in the lamps or said gas or gas mixtureto emit electromagnetic radiation extending over a radiation spectrum,and comprising, in accordance with the invention, the steps ofdetermining the magnitude of the pressure or partial pressure of saidfill by selecting, within a spectral portion of said radiation spectrum,at least one spectral line having an intensity which is largelydependent upon pressure of said gases or gas mixtures for said electriclamps or radiators; and measuring the intensity or intensities of saidat least one so selected spectral line or lines, to thereby determinethe pressure or partial pressure of the gas or the corresponding gascomponent.
 19. The method of claim 18, wherein the gas or gas mixturecomprises argon, and said selecting step comprises selecting thespectral line having the wavelength γ=763.5 nm.
 20. The method of claim18, wherein said selection step comprises selecting two spectral lineswhich are close together, and said measuring step comprisesforming aquotient of the intensity of said two closely adjacent spectral lines,so that noise signals and in-phase interference signals are largelyeliminated by the adjacent position of said spectral lines in the courseof the formation of the quotient.
 21. The method of claim 20, whereinthe difference in the wavelengths of the two spectral lines is less thanabout 100 nm.
 22. The method of claim 21, wherein the difference is lessthan 50 nm.
 23. The method of claim 20, wherein the gas or gas mixturecomprises argon, and said selection step comprises selecting thespectral line of the argon having the wavelength 738.4 nm, saidwavelength being used to form said quotient.
 24. The method of claim 18,wherein said step of exciting the gas mixture comprises exciting the gasmixture to generate to the extent of generating a glow discharge withinthe respective electric lamp or radiator.
 25. The method of claim 18,wherein said step of exciting the gas or gas components by means of agas discharge comprises generating electromagnetic energy of highfrequency and applying said so generated high-frequency energy to saidgas or gas components.
 26. A method for spectroscopically detectingimpurities in gases, especially noble gases, or gas mixtures, forelectric lamps or radiators, and forming a fill for said lamps orradiators, said method being integrated into the production process in aproduction line for discharge lamps,comprising the steps of:a) before adischarge vessel of a discharge lamp is filled, spectroscopicallymeasuring, by means of a specimen discharge inside the gas system of thelamp production line, said fill to monitor the gas system of theproduction line for impurities; b) inserting electrodes into thedischarge vessel, and then spectroscopically measuring, by means of aspecimen discharge inside the discharge vessel and after the insertionof the electrodes therein to, the spectral lines emitted from adischarge, to thereby monitor the electrode system and the wall of thedischarge vessel for impurities; c) filling and closing the dischargevessel and then spectroscopically measuring, by means of a specimendischarge inside the discharge vessel, to check whether the impuritiesin the interior of the finished lamp are within a predeterminedtolerance range; and wherein said spectroscopic measurement comprisescarrying out the steps ofd-1) determining any possibly presentimpurities in said gases or gas mixtures by selecting, within a spectralportion of said radiation spectrum, at least one spectral line having anintensity which is largely independent of pressure in the relevantregion of pressures of gases or gas mixtures, for said electric lamp orlamps or radiators, and measuring the intensity of the so selectedspectral line or lines and thereby determining any possibly presentimpurities; or d-2) determining the magnitude of the pressure or partialpressure of said fill by selecting, within a spectral portion of saidradiation spectrum, at least one spectral line having an intensity whichis largely dependent upon pressure of said gases or gas mixtures forsaid electric lamps or radiators; and measuring the intensity orintensities of said at least one so selected spectral line or lines, tothereby determine the pressure or partial pressure of the gas or thecorresponding gas component.
 27. The method of claim 26, furthercomprising the following additional method stepe) spectroscopicallymeasuring the pressure of the fill inside the vessel as set forth instep d-2) by means of specimen discharge inside the discharge vesselafter the filling and closure of the discharge vessel; and determiningwhether the cold fill pressure in the interior of the discharge vesselof the finished lamp is within a predetermined tolerance range.
 28. Themethod of claim 26, comprising the following additional method stepf)interrupting production, before the discharge vessel is filled andclosed, if the measured values determined by at least one of the methodsteps a) and b) are outside a predeterminable tolerance range.
 29. Themethod of claim 26, comprising the following additional method stepg)rejecting an affected discharge vessel if the measurement valuesdetermined by at least one of method steps c) and d) are outside apredeterminable tolerance range.
 30. The method of claim 26, comprisingperforming the specimen discharge of method step a) in a specimen vesselconnected to a vacuum ring line.
 31. The method of claim 26, comprisingperforming the specimen discharges of method steps b) and c) between theelectrodes of the specimen discharge vessel.
 32. An electric lamp orradiator test apparatus carrying out a method of detection of impuritiesin a lamp fill formed of gases, or gas mixtures, or of fill pressure, inwhichany possibly present impurities in said gases or gas mixtures aredetermined by selecting, within a spectral portion of said radiationspectrum, at least one spectral line having an intensity which islargely independent of pressure in the relevant region of pressures ofgases or gas mixtures, for said electric lamp or lamps or radiators, andmeasuring the intensity of the so selected spectral line or lines andthereby determining any possibly present impurities; or the magnitude ofthe pressure or partial pressure of said fill is determined byselecting, within a spectral portion of said radiation spectrum, atleast one spectral line having an intensity which is largely dependentupon pressure of said gases or gas mixtures for said electric lamps orradiators; and measuring the intensity or intensities of said at leastone so selected spectral line or lines, to thereby determine thepressure or partial pressure of the gas or the corresponding gascomponent; said apparatus comprisinga vessel (1; 15), in which the gasor gas mixture and the impurities possibly contained therein arelocated; an energy supply unit (7, 16), which is connected to the vessel(1) via a coupling device (3, 4, 5) and generates the gas discharge; aspectroscopic measurement device (12; 18-22), which measures theintensity or intensities of said spectral line or lines generated bysaid discharge; an evaluation device (13; 23, 24) coupled to thespectroscopic measuring device (12, 18-22), which from the measuredvalues ascertains the concentration of the impurities or the pressure orpartial pressure of the gas or gas component by selecting, respectively,at least one spectral line which is pressure-independent or,respectively, a plurality of spectral lines independent of pressure, andmeasuring the intensity or intensities of the selected spectral line orlines; and a pumping, gas fill, and pressure control and measuringsystem (30) coupled to said lamp, lamps, radiators and providing saidfill, under controlled pressure.
 33. The apparatus of claim 32, whereinthe energy supply unit comprises a high-frequency generator (7; 16),thecoupling device comprises a high-voltage transformer (5) and twohigh-frequency (HF) electrodes (3, 4), the HF electrodes being connectedto the secondary winding (8) of the transformer (5); and thehigh-frequency generator (7) being connected to the primary winding (6)of the high-voltage transformer (5).
 34. The apparatus of claim 32,wherein the vessel comprises a discharge vessel of a discharge lamp(15), two lamp electrodes being located in the interior of the dischargevessel, each being connected to power supply leads extending to theoutside in gastight manner and in turn being connected to the energysupply unit (16), so that the lamp electrodes are a component of thecoupling device.
 35. The apparatus of claim 33, wherein at least one ofthe HF electrodes (3, 4) is located on the outer wall of the vessel. 36.The apparatus of claim 35, wherein the vessel comprises the lamp bulb ofan incandescent lamp, on the outer wall of which a first HF electrode ismounted, an incandescent coil (25) being located in the interior of thebulb, the coil being coupled to the high-frequency generator (7), sothat the incandescent coil acts as a second HF electrode.
 37. Theapparatus of claim 32, wherein the spectroscopic measurement devicecomprises a spectrometer (12), the radiation being spectroscopicallyanalyzed in regard to its spectral components and providing an analysisoutput corresponding to their respective intensity.
 38. The apparatus ofclaim 37, wherein the evaluation device (3; 23, 24) comprises acomputer, which receives and reads the analysis output and processes andsaid output and, as a result, outputs the value of at least one of thegas pressure, and the concentration of the impurity or impurities.